Hearing aid comprising an array of microphones

ABSTRACT

Hearing aid for improving the hearing ability of the hard of hearing, comprising an array of microphones, the electrical output signals of which are fed to at least one transmission path belonging to an ear. Means are provided for deriving two array output signals from the output signals of the microphones, the array having two main sensitivity directions running at an angle with respect to one another and each of which is associated to an array output signal. Each array output signal is fed to its own transmission path belonging to one ear of a person who is hard of hearing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hearing aid for improving the hearing abilityof the hard of hearing, comprising an array of microphones, theelectrical output signals of which are fed to at least one transmissionpath belonging to an ear.

2. Description of the Related Art

A device of this type is known from the article entitled “Development ofa directional hearing instrument based on array technology” published inthe “Journal of the Acoustical Society of America”, Vol. 94, Edition 2,Pt. 1, pages 785–798, August 1993.

It is generally known that loss of hearing in people can be compensatedfor by means of a hearing aid, in which amplification of the receivedsound is used. In environments with background noise, for example whenseveral people are speaking at once, as is the case at a cocktail party,the hearing aid amplifies both the desired speech and the noise, as aresult of which the ability to hear is not improved.

In the abovementioned article the authors describe an improvementproposal. The hearing aid disclosed in the article consists of an arrayof, for example, five directional microphones, as a result of which itis possible for the person who is hard of hearing to understand someonewho is speaking directly opposite him or her. The background noise whichemanates from other directions is suppressed by the array.

From U.S. Pat. No. 4,956,867 an apparatus for suppressing signals fromnoise sources surrounding a target source is known. This apparatuscomprises a receiving array including two microphones spaced apart by adistance. The outputs of the microphones are combined such that aprimary signal channel and a noise signal channel are obtained. Theoutputs of the channels are substrated for cancelling the noise from theprimary signal channel.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a hearing aid of the typementioned in the preamble with which the abovementioned disadvantagesare avoided and the understandability of the naturalness of thereproduction improved in a simple manner.

Said aim is achieved according to the invention in that means areprovided for deriving two array output signals from the output signalsof the microphones, the array having two main sensitivity directionsrunning at an angle with respect to the main axis of the array, and eachof which is associated to an array output signal, and in that each arrayoutput signal is fed to its own transmission path one to the left earand the other to the right ear of a person who is hard of hearing.

With this arrangement the signals from the microphones of the array arecombined to give a signal for the left ear and a signal for the rightear. The array has two main sensitivity directions or main lobes runningat an angle with respect to one another, the left ear signal essentiallyrepresenting the sound originating from the first main sensitivitydirection and the right ear signal representing that from the other mainsensitivity direction. The array output signals, that is to say the leftear signal and the right ear signal, are fed via their own transmissionpath to the left ear and the right ear, respectively. Amplification ofthe signal and conversion of the electrical signal into a sound signalis employed in said transmission path.

The different main lobes introduce a difference in level between thesignals to be fed to the ears. It has been found that it is not onlypossible to localize sound sources better, but that background noise isalso suppressed as a result of the directional effect, as a result ofwhich the understandability of speech is improved despite the existingnoise.

The array can advantageously be mounted on the front of a spectacleframe and/or on the arms or springs.

In the case of an embodiment which is preferably to be used, eachspectacle arm is also provided with an array of microphones, the outputsignals from the one array being fed to the one transmission path andthe output signals from the other array being fed to the othertransmission path.

What is achieved by this means is that understandability is improved notonly at high frequencies in the audible sound range but also atrelatively low frequencies.

Further embodiments of the invention are described in the subsidiaryclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference tothe drawings. In the drawings:

FIG. 1 shows an embodiment of the hearing aid according to theinvention;

FIG. 2 shows a more detailed embodiment of the hearing aid according tothe invention;

FIG. 3 shows another embodiment of the hearing aid according to theinvention;

FIG. 4 shows an embodiment of the hearing aid according to FIG. 4 inwhich a combination of arrays is used, which embodiment is preferably tobe used;

FIG. 5 shows a polar diagram of a combined array from FIG. 1 at 500 and1000 Hz;

FIG. 6 shows a polar diagram of an embodiment from FIG. 1 at 2000 and4000 Hz; and

FIG. 7 shows the directional index of the embodiment in FIG. 4 as afunction of the frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The hearing aid according to the invention comprises an array ofmicrophones. Said array can have any shape.

Said array has two array output signals which are each fed along theirown transmission path, one to the left ear and the other to the rightear of the person hard of hearing. In said transmission pathamplification and conversion of the electrical signal from the array tosound vibrations are employed in the conventional manner.

The array has two main sensitivity directions running at an angle withrespect to one another, the various features being such that the firstarray output signal is essentially a reflection of the sound from thefirst main sensitivity direction, whilst the second array output signalessentially represents the sound from the second main sensitivitydirection. As a result the left ear as it were listens in a restrictedfirst main sensitivity direction, whilst the right ear listens in thesecond main sensitivity direction.

The main sensitivity directions associated with the array output signalscan be achieved by focusing or bundling the microphone signals.

The array of microphones can be attached in a simple manner to spectacleframes. FIG. 1 shows an embodiment of an array of microphones on thefront of the spectacle frames, bundling being employed.

In FIG. 1 the head of a person hard of hearing is indicateddiagrammatically by reference number 1. The spectacles worn by thisperson as shown diagrammatically by straight lines, which spectaclesconsist, in the conventional manner, of a front 2 and two spectacle armsor springs 3, 4.

The main lobe 5 for the left ear and the main lobe 6 for the right earare also shown in FIG. 1 as ellipses. Said main lobes are at an anglewith respect to one another and with respect to the main axis 7 of thespectacles.

As a result of the main lobes used above and the separate assignmentthereof to the ears, a difference between the level of the array outputsignals is artificially introduced depending on the location of thesound source and also for the noise. As a result of said artificialdifference in the levels of the array output signals, the person hard ofhearing is able to localize the sound source, but is has been found thatsaid difference also improves the understandability of speech in thepresence of noise.

Positioning the array of microphones on one or both of the spectaclearms is also advantageous.

The association of the array output signals to the associated main lobesof the array can be achieved in a simple manner by means of a so-calledparallel or serial construction.

In the case of the parallel construction, the means for deriving thearray output signals comprise a summing device, the microphone outputsignals being fed to the inputs of said summing device via a respectivefrequency-dependent or frequency-independent weighting factor device. Anarray output signal can then be taken off at the output of the summingdevice. A main sensitivity direction associated with the relevant arrayoutput signal can be obtained by sizing the weighting factor devices.

In the case of the so-called serial construction, the means for derivingthe array output signals contain a number of summing devices andweighting factor devices, the weighting factor devices in each casebeing connected in series with the input and output of the summingdevices. With this arrangement one outermost microphone is connected toan input of a weighting factor device, the output of which is thenconnected to an input of a summing device. The output of the microphoneadjacent to the said outermost microphone is connected to the input ofthe summing device. The output of the summing device is connected to theinput of the next weighting factor device, the output of which isconnected to the input of the next summing device. The output of thenext microphone is, in turn, connected to the other input of thissumming device.

This configuration is continued as far as the other outermost microphoneof the array. An array output signal, for example the left ear signal,can be taken off from the output of the last summing device, the inputof which is connected to the output of the last-mentioned outermostmicrophone. It could also be possible to derive the array output signalfrom the output of the said last summing device via a further weightingfactor device.

In a further development, the weighting factor device comprises a delaydevice, optionally supplemented by an amplitude-adjustment device.

In another development, the weighting factor device consists of a phaseadjustment device, optionally supplemented by an amplitude-adjustmentdevice.

FIG. 2 shows the parallel construction with delay devices. Themicrophones 8, 9, 10, 11 and 12 are shown on the right of FIG. 2, whichmicrophones are connected by a line in the drawing to indicate that itis an array that is concerned here. The outputs of the microphones 8–12are connected to the inputs of the respective delay devices 13, 14, 15,16 and 17. The outputs of the said delay devices 13–17 are connected tothe inputs of the summing device 18, at the output of which an arrayoutput signal, for example a left ear signal, can be derived. Anamplitude-adjustment device, which can consist of an amplifier or anattenuator, can be incorporated, in a manner which is not shown, in eachpath between a microphone and an input of the summing device.Preferably, the signal of the n^(th) microphone is delayed by a periodnτ_(t). FIG. 2 shows that the output signal from the microphone 8 is fedto the input of the summing device 18 with a delay period O, whilst theoutput signal from the microphone 9 is fed to the next input of thesumming device 18 with a delay τ_(t). The corresponding delays apply inthe case of the microphones 10, 11 and 12; that is to say delay periodsof 2τ_(t), 3τ_(t) and 4τ_(t) respectively. The delay period τ_(t) ischosen such that sound emanating from the direction which makes an angleof θ with respect to the main axis of the array is summed in phase.Then: τ_(t)=dsin θ/c, where d is the distance between two microphonesand c is the wave propagation rate.

A similar arrangement can be designed for the right ear signal.

FIG. 3 shows the so-called serial construction with delay devices.

In the case of this embodiment shown a series circuit of 4 delay devices19–22 and 4 summing devices 37–40 is used. The delay devices and summingdevices are connected alternately in series. The microphone 12 isconnected to the input of the delay device 21, whilst the outputs of themicrophones 8–11 are connected to the respective summing devices 37–40.

With this embodiment as well the signal from the microphone 12 isdelayed by a delay period of 4 times τ_(t), if each delay deviceproduces a delay of τ_(t). After adding in the summing device 40, theoutput signal from the microphone 11 is delayed by a delay period of 3times τ_(t). Corresponding delays apply in respect of the microphones 9and 10. The output signal from the microphone 8 is not delayed. Ifdesired, a further delay device can be incorporated behind the summingdevice 37.

With this so-called serial construction as well it is possible toincorporate amplitude-adjustment devices in the form of amplifiers orattenuators in each part of the series circuit, eachamplitude-adjustment device being associated with an output signal froma specific microphone in the array. The delay device used can simply bean all-pass filter of the first order, which can be adjusted by means ofa potentiometer.

A microphone array 14 cm long can be used as a practical embodiment. Asa consequence of the means described above for deriving the outputsignals from the microphones which are each associated with one mainsensitivity direction, the microphones used can be very simplemicrophones of omnidirectional sensitivity. If desired, cardioidmicrophones can be used to obtain additional directional sensitivity.

If the angle between the two main sensitivity directions or main lobesbecomes greater, the difference between the audible signals, i.e. theinter-ear level difference, will become greater. Consequently thelocalizability will in general become better.

However, as the said angle between the main lobes becomes greater, theattenuation of a sound signal will increase in the direction of a mainaxis of the array. The choice of the angle between the main lobes willthus, in practice, be a compromise between a good inter-ear leveldifference and an acceptable attenuation in the main direction of thearray. This choice will preferably be determined experimentally.

Furthermore, on enlarging the angle between the main lobes, the mainlobes will each be split into two lobes beyond a certain angle. Thisphenomenon can be avoided by use of an amplitude-weighting function forthe microphone signals.

In the case of an embodiment of the invention that is preferably to beused, an array attached to the front of the spectacle frames and twoarrays, each attached to one arm of the spectacles, are used. An examplewith eleven microphones is shown in FIG. 4. The microphones 26, 27 and28, which form the left array, are attached to the left arm of thespectacles and the microphones 34, 35 and 36 of the right array areattached to the right arm of the spectacles. The microphones 29–33 areattached to the front of the spectacle frames.

The signals from the microphones 29–33 are fed in the manner describedabove to the transmission paths for the left and the right ear,respectively. The signals from the microphones 26, 27 and 28 are coupledto the transmission path for the left ear, whilst the signals from themicrophones 34–36 are fed via the other transmission path to the rightear.

At high frequencies an inter-ear level difference is created with theaid of bundling the array at the front of the spectacle frames and theshadow effect of the arrays on the arms of the spectacles has aninfluence. At low frequencies an inter-ear time difference is created bymeans of the arrays on the arms of the spectacles. An inter-ear timedifference is defined as the difference in arrival time between thesignals at the ears as a consequence of the difference in propagationtime.

FIG. 5 shows the directional characteristics of the combination ofarrays in FIG. 4 at a frequency of 500 Hz, indicated by a dash-and-dotline, and at 1000 Hz, indicated by a continuous line. The directionalcharacteristics in FIG. 5 are obtained with the arrays on the arms ofthe spectacles. The array on the front of the spectacles is thusswitched off since it yields little additional directional effect at lowfrequencies. In this way an inter-ear time difference is thus created.

FIG. 6 shows the directional characteristics of the combination ofarrays at 2000 Hz, indicated by a dash-and-dot line, 2 and at 4000 Hz,indicated by a continuous line. In the mid and high frequency region ofthe audible sound range the main lobes are directed at 11°, so that onceagain an inter-ear level difference is created.

FIG. 7 shows the directivity index as a function of the frequency for 3optimized frequency ranges. The continuous line applies for the lowfrequencies, optimized at 500 Hz. The broken line applies foroptimization at 4000 Hz and the dash-and-dot line for optimization at2300 Hz.

It is also pointed out that an inter-ear level difference can also beproduced with the arrays on the arms of the spectacles as with the arrayon the front of the spectacle frames.

1. A hearing aid for improving the hearing ability of a user,comprising: an array of microphones, each producing a respectivemicrophone output signal; each left and right summing structures, eachreceiving as inputs a subset of the microphone output signals, beingconstructed so as to generate left and right array output signals,respectively; and left and right transmissions paths, each carrying acorresponding one of the left and right array output signals to acorresponding ear of the user; wherein each of the left and rightsumming structures acts on a corresponding said subset of microphoneoutput signals so that the different left and right array output signalscorrespond respectively to two distinct main sensitivity directions thatare associated with two distinct main sensitivity lobes and lie at anangle to one another, which angle deviates from 0°.
 2. The hearing aidaccording to claim 1, wherein at least part of the array is mounted onat least one of a front and one or two temples of a pair of spectacles.3. The hearing aid according to claim 2, each of said two distinct mainsensitivity directions being at an angle, which deviates from 0°, tosaid temples.
 4. The hearing aid according to claim 3, wherein each saidtemple of the pair of spectacles is provided with those of the array ofmicrophones that produce a respective one of the subsets of themicrophone output signals.
 5. The hearing aid according to claim 1,wherein each of the left and right summing structures comprises asumming device, the summing device receiving as inputs weighted versionsof the microphone output signals produced by corresponding weightingfactor devices.
 6. The hearing aid according to claim 5, wherein theweighting factor device comprises a delay device.
 7. The hearing aidaccording to claim 6, wherein the weighting factor device comprises anamplitude-adjustment device.
 8. The hearing aid according to claim 5,wherein the weighting factor device comprises a phase-adjustment device.9. The hearing aid according to claim 8, wherein the weighting factordevice further comprises an amplitude-adjustment device.
 10. The hearingaid according to claim 1, wherein each of the left and right summingstructures comprises a series circuit of weighting factor device andsumming device pairs; wherein in each said pair, the summing devicereceives, as a first input, an output of the corresponding weightingfactor device, and the summing device receives, as a second input, arespective one of the microphone output signals; in each but a first ofthe pairs an input of the weighting factor device is provided by anoutput of a preceding one of the summing devices in the series circuit,and in the first of the pairs the input of the weighting factor deviceis provided by the microphone output signal of an outermost one of themicrophones; and an output of the summing device of a last of the seriescircuit pairs provides a respective one of the left and right arrayoutput signals.
 11. The hearing aid according to claim 10, wherein thearray output signal is derived via a further weighting factor device.12. The hearing aid according to claim 11, wherein the weighting factordevice comprises a delay device.
 13. The hearing aid according to claim11, wherein the weighting factor device comprises a phase-adjustmentdevice.
 14. The hearing aid according to claim 10, wherein the weightingfactor device comprises a delay device.
 15. The hearing aid according toclaim 10, wherein the weighting factor device comprises aphase-adjustment device.
 16. The hearing aid of claim 1, wherein each ofthe left and right summing structures operates in afrequency-independent manner so that each of the main sensitivitydirections is frequency-independent.
 17. The hearing aid of claim 16,wherein each of the microphones is omnidirectional.
 18. The hearing aidaccording to claim 17, wherein at least part of the array is mounted ona temple of a pair of spectacles and said two main distinct sensitivitydirections being at an angle, which deviates from 0°, to said temple.19. The hearing aid according to claim 18, wherein said spectacles havetwo temples and each of said temples is provided with those of the arrayof microphones that produce a respective one of the subsets of themicrophone output signals.
 20. The hearing aid of claim 1, wherein eachof the main sensitivity directions also lies at an angle to a main axisof the array.
 21. The hearing aid of claim 1, wherein at least one ofthe microphones is omnidirectional.
 22. The hearing aid of claim 1,wherein each of the microphones is omnidirectional.
 23. A hearing aidfor improving the hearing ability of a user, comprising: an array ofmicrophones, each producing a respective microphone output signal; meansfor converting a first subset of the microphone output signals to a leftarray output signal; means for converting a second subset of themicrophone output signals to a right array output signal; left and righttransmissions paths, each carrying a corresponding one of the left andright array output signals to a corresponding ear of the user; whereineach means for converting acts on a corresponding said subset ofmicrophone output signals so that the different left and right arrayoutput signals correspond respectively to two distinct main sensitivitydirections that are associated with two distinct main sensitivity lobesand lie at an angle to one another, which angle deviates from 0°. 24.The hearing aid of claim 23, wherein at least one of the microphones isomnidirectional.
 25. The hearing aid of claim 23, wherein each of themicrophones is omnidirectional.
 26. The hearing aid of claim 23, whereineach of the main sensitivity directions also lies at an angle to a mainaxis of the array.
 27. The hearing aid of claim 23, wherein each meansfor converting operates in a frequency-independent manner so that eachof the main sensitivity directions is frequency-independent.
 28. Thehearing aid of claim 27, wherein each of the microphones isomnidirectional.
 29. The hearing aid according to claim 28, wherein atleast part of the array is mounted on a temple of a pair of spectaclesand said two main distinct sensitivity directions being at an angle,which deviates from 0°, to said temple.
 30. The hearing aid according toclaim 29, wherein said spectacles have two temples and each of saidtemples is provided with those of the array of microphones that producea respective one of the subsets of the microphone output signals. 31.The hearing aid according to claim 23, wherein at least part of thearray is mounted on a front of a pair of spectacles.
 32. The hearing aidaccording to claim 23, wherein at least part of the array is mounted ona temple of a pair of spectacles and said two main distinct sensitivitydirections being at an angle, which deviates from 0°, to said temple.33. The hearing aid according to claim 32, wherein said spectacles havetwo temples and each of said temples is provided with those of the arrayof microphones that produce a respective one of the subsets of themicrophone output signals.
 34. A hearing aid for improving the hearingability of a user, comprising: an array of microphones, each producing arespective microphone output signal; left and right summing structures,each receiving as inputs a subset of the microphone output signals, eachbeing constructed so as to generate left and right array output signals,respectively; left and right transmissions paths, each carrying acorresponding one of the left and right array output signals to acorresponding ear of the user; wherein each of the left and rightsumming structures acts on its subset of microphone output signals sothat the different left and right array output signals correspondrespectively to two distinct main sensitivity directions that areassociated with two distinct main sensitivity lobes and lie at an angleto one another, which angle deviates from 0°; and wherein each of theleft and right summing structures operates so that the array outputsignals include low, mid, and high audio frequency components.
 35. Thehearing aid of claim 34, wherein at least one of the microphones isomnidirectional.
 36. The hearing aid of claim 34, wherein each of themicrophones is omnidirectional.
 37. The hearing aid of claim 34, whereineach of the main sensitivity directions also lies at an angle to a mainaxis of the array.
 38. The hearing aid of 34, wherein the mid-frequencycomponents include signals having a frequency of 2000 Hz.
 39. Thehearing aid of 38, wherein the high-frequency components include signalshaving a frequency of 4000 Hz.
 40. The hearing aid of 39, wherein thelow-frequency components include signals having a frequency of 500 Hz.41. The hearing aid of claim 40, wherein each of the microphones isomnidirectional.
 42. The hearing aid according to claim 41, wherein atleast part of the array is mounted on a temple of a pair of spectaclesand said two main distinct sensitivity directions being at an angle,which deviates from 0°, to said temple.
 43. The hearing aid according toclaim 42, wherein said spectacles have two temples and each of saidtemples is provided with those of the array of microphones that producea respective one of the subsets of the microphone output signals. 44.The hearing aid according to claim 34, wherein at least part of thearray is mounted on a front of a pair of spectacles.
 45. The hearing aidaccording to claim 34, wherein at least part of the array is mounted ona temple of a pair of spectacles and said two main distinct sensitivitydirections being at an angle, which deviates from 0°, to said temple.46. The hearing aid according to claim 45, wherein said spectacles havetwo temples and each of said temples is provided with those of the arrayof microphones that produce a respective one of the subsets of themicrophone output signals.
 47. A hearing aid for improving the hearingability of a user, comprising: an array of microphones, each producing arespective microphone output signal; means for converting a first subsetof the microphone output signals to a left array output signal thatcorresponds to a first main sensitivity direction that is associatedwith a first main sensitivity lobe; means for converting a second subsetof the microphone output signals to a right array output signal thatcorresponds to a second main sensitivity direction that is associatedwith a second main sensitivity lobe and lies at an angle to the firstmain sensitivity direction, which angle deviates from 0°; and left andright transmissions paths, each carrying a corresponding one of thedifferent left and right array output signals to a corresponding ear ofthe user; wherein each means for converting operates so that the arrayoutput signals include low, mid, and high audio frequency components.48. The hearing aid of claim 47, wherein at least one of the microphonesis omnidirectional.
 49. The hearing aid of claim 47, wherein each of themicrophones is omnidirectional.
 50. The hearing aid of claim 47, whereineach of the main sensitivity directions also lie at an angle to a mainaxis of the array.
 51. The hearing aid of 47, wherein the mid-frequencycomponents include signals having a frequency of 2000 Hz.
 52. Thehearing aid of 51, wherein the high-frequency components include signalshaving a frequency of 4000 Hz.
 53. The hearing aid of 51, wherein thelow-frequency components include signals having a frequency of 500 Hz.54. The hearing aid of claim 53, wherein each of the microphones isomnidirectional.
 55. The hearing aid according to claim 54, wherein atleast part of the array is mounted on a temple of a pair of spectaclesand said two main distinct sensitivity directions being at an angle,which deviates from 0°, to said temple.
 56. The hearing aid according toclaim 55, wherein said spectacles have two temples and each of saidtemples is provided with those of the array of microphones that producea respective one of the subsets of the microphone output signals. 57.The hearing aid according to claim 47, wherein at least part of thearray is mounted on a front of a pair of spectacles.
 58. The hearing aidaccording to claim 47, wherein at least part of the array is mounted ona temple of a pair of spectacles and said two main distinct sensitivitydirections being at an angle, which deviates from 0°, to said temple.59. The hearing aid according to claim 58, wherein said spectacles havetwo temples and each of said temples is provided with those of the arrayof microphones that produce a respective one of the subsets of themicrophone output signals.